Heavy Metal Bioaccumulation and Oxidative Stress Profile in Brachidontes pharaonis (Bivalvia: Mytilidae) from the Tunisian Coast: Insight into Its Relevance as Bioindicator of Marine Pollution

Elevated trace element concentrations in Arabian scallops, Natal rock oysters, and Intermediate clams in the Persian Gulf

BACKGROUNDS

This study aimed to quantify trace element concentrations in Arabian scallops (Mimachlamys sanguinea), Natal rock oysters (Saccostrea cucullata), and Intermediate clams (Tivela damaoides). These elements accumulate over time from water, food, and sediment, potentially leading to toxicity.

MATERIALS AND METHODS

Specimens were collected from coastal waters around Larak Island, processed, and analyzed for trace elements including copper (Cu), iron (Fe), cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), zinc (Zn), vanadium (V), magnesium (Mg), manganese (Mn), selenium (Se), nickel (Ni), and cobalt (Co). The samples were ashed, digested, and then analyzed using inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

The findings revealed that Fe levels were highest in T. damaoides, significantly exceeding those in M. sanguinea (p < 0.05). Cd concentrations were significantly higher in M. sanguinea compared to S. cucullata and T. damaoides (p < 0.05). Zn, Mn, Ni, Pb, V, Co, Hg, Cu, As, and Se showed no significant interspecies differences (p > 0.05). However, significant variations were noted for Mg with T. damaoides showing the highest levels markedly more significant than those observed in M. sanguinea (p < 0.05). Comparison with WHO/FAO standards showed that Pb levels in the soft tissues of all three bivalve species exceeded permissible limits, though other metals were within safe consumption levels.

CONCLUSION

This study revealed that lead concentrations in the soft tissues of bivalves exceeded WHO/FAO safety limits, indicating a potential health risk. These findings emphasize the necessity of monitoring trace element contamination in bivalves to ensure seafood safety and protect public health.

Heavy metal accumulation and interaction dynamics in Brachidontes pharaonis: a bioindicator study in the Red Sea

This work evaluates utilizing the native mussel Brachidontes pharaonis as a bioindicator and sentinel organism for monitoring heavy metals Cu, Zn, and Cd along the Red Sea coast of Egypt. Samples were collected from four coastal locations, and the concentrations of heavy metals in the mussels' tissues, shells, seawater, and sediments were analyzed. Subsequently, bioassay experiments were conducted by exposing the organisms to single, binary, and tertiary metal mixtures, and the accumulation of heavy metals was determined to elucidate the dynamics of metal-metal interactions. Field samples revealed significant variations in heavy metal concentrations in the mussels' soft tissues across different locations, with Zn ranging from 58.1 to 121.0 µg/g dw (dry weight), Cu ranging between 18.3 and 36.7 µg/g dw, and Cd ranging from 0.3 to 1.04 µg/g dw. Conversely, the shells exhibited minimal spatial variations, with much lower contents of Cu (ranging from 1.9 to 2.8 µg/g dw) and Zn (ranging from 1.8 to 1.9 µg/g dw). However, the shells accumulated Cd at higher levels (ranging from 1.4 to 2.1 µg/g dw) compared to the soft tissues. Following a 96-h bioassay experiment, the soft tissues displayed a linear accumulation of metals with increasing exposure dose, with Cd showing the highest accumulation rate (approximately threefold) followed by Zn (twofold) and Cu (1.7-fold). In binary and tertiary exposures, the metals exhibited a general antagonistic interaction, affecting each other's accumulation. On the other hand, the accumulation of heavy metals in the shells after the 96-h bioassay exposure did not follow a consistent linear pattern, suggesting that accumulation during this short experimental period occurs primarily through adsorption rather than the biological pathway.

Bioindicator responses to extreme conditions: Insights into pH and bioavailable metals under acidic metal environments

Acid mine drainage (AMD) caused environmental risks from heavy metal pollution, requiring treatment methods such as chemical precipitation and biological treatment. Monitoring and adapting treatment processes was crucial for success, but cost-effective pollution monitoring methods were lacking. Using bioindicators measured through 16S rRNA was a promising method to assess environmental pollution. This study evaluated the effects of AMD on ecological health using the ecological risk index (RI) and the Risk Assessment Code (RAC) indices. Additionally, we also examined how acidic metal stress affected the diversity of bacteria and fungi, as well as their networks. Bioindicators were identified using linear discriminant analysis effect size (LEfSe), Partial least squares regression (PLS-R), and Spearman analyses. The study found that Cd, Cu, Pb, and As pose potential ecological risks in that order. Fungal diversity decreased by 44.88% in AMD-affected areas, more than the 33.61% decrease in bacterial diversity. Microbial diversity was positively correlated with pH (r = 0.88, p = 0.04) and negatively correlated with bioavailable metal concentrations (r = -0.59, p = 0.05). Similarly, microbial diversity was negatively correlated with bioavailable metal concentrations (bio_Cu, bio_Pb, bio_Cd) (r = 0.79, p = 0.03). Acidiferrobacter and Thermoplasmataceae were prevalent in acidic metal environments, while Puia and Chitinophagaceae were identified as biomarker species in the control area (LDA>4). Acidiferrobacter and Thermoplasmataceae were found to be pH-tolerant bioindicators with high reliability (r = 1, P < 0.05, BW > 0.1) through PLS-R and Spearman analysis. Conversely, Puia and Chitinophagaceae were pH-sensitive bioindicators, while Teratosphaeriaceae was a potential bioindicator for Cu-Zn-Cd metal pollution. This study identified bioindicator species for acid and metal pollution in AMD habitats. This study outlined the focus of biological monitoring in AMD acidic stress environments, including extreme pH, heavy metal pollutants, and indicator species. It also provided essential information for heavy metal bioremediation, such as the role of omics and the effects of organic matter on metal bioavailability.

Seasonal Monitoring of Heavy Metal Pollution in Water and Zebra Mussels Dreissena polymorpha as a Potential Bioindicator Species from Lake Habitat

In aquatic ecosystem, metal pollution is an important environmental hazard. Mussels as a bioindicator species are often used for assessment the presence of potentially toxic metals. Hence, the present study aimed to assess the effect of seasonal variations on some heavy metals (Cd, Cr, Pb, As, Zn and Cu) accumulation in water and Dreissena polymorpha from lake habitat. Our result indicated that Zn accumulated at a very high level in the zebra mussels while As accumulated at a high level in water samples. Seasonal variations significantly affected Cu concentration in the water samples (P < 0.05) while Cr concentration in the mussel samples was significantly affected by seasonal variations (P < 0.05). According to the water analysis, mean concentrations of metals are below the maximum limits established by the World Health Organization and USEPA, except As. Overall, our data emphasize anthropogenic pollution in the Turkish aquatic environment and confirm the use of D. polymorpha as a prospective biomonitor for metal polluted sites'.

Growth retardation and suppression of ubiquitin-dependent catabolic processes in the brackish water clam Corbicula japonica in response to salinity changes and bioaccumulation of toxic heavy metals

The brackish water clam (Corbicula japonica) is constantly exposed to stressful salinity gradients and high levels of heavy metals in the freshwater-saltwater interface of estuary environments, which are introduced from upstream regions and land. To identify the key molecular pathways involved in the response to salinity changes and heavy metal bioaccumulation, we obtained the transcriptomes of C. japonica inhabiting different salinities and heavy metal distributions in Gwangyang Bay (Korea) using RNA sequencing. Among a total of 404,486 assembled unigenes, 5534 differentially expressed genes were identified in C. japonica inhabiting different conditions, 1549 of which were significantly upregulated and 1355 were significantly downregulated. Correlation analyses revealed distinct gene expression patterns between the low and high conditions of salinity and heavy metal bioaccumulation. Functional annotation revealed significant downregulation of genes involved in "ubiquitin-dependent protein catabolic process," "tricarboxylic acid cycle," and "intracellular protein transport" in C. japonica from the high condition compared to the low condition. Transcription and translation pathways were significantly enriched in the high condition. Additionally, upon comparison of the low and high conditions by qRT-PCR and proteasome enzyme activity analyses, our findings demonstrated that environmental stress could suppress the ubiquitin-proteasome complex (UPC). Additionally, transcriptomic changes under high salinity stress conditions may be related to an increase in cellular protection by defense enzymes, which leads to more energy being required and a disruption of energy homeostasis. Ultimately, this could cause growth retardation in the clam C. japonica. In summary, this study provides the first evidence of UPC suppression induced by a combination of high salinity and heavy metal bioaccumulation stress in C. japonica, which could compromise the survival and growth of estuarine bivalves.

Quantitative determination of heavy metal contaminants in edible soft tissue of clams, mussels, and oysters

Aquatic environments are important sources of healthy and nutritious foods; however, clams, mussels, and oysters (the bivalves most consumed by humans) can pose considerable health risks to consumers if contaminated by heavy metals in polluted areas. These organisms can accumulate dangerously high concentrations of heavy metals (e.g., Cd, Hg, Pb) in their soft tissues that can then be transferred to humans following ingestion. Monitoring contaminants in clams, mussels and oysters and their environments is critically important for global human health and food security, which requires reliable measurement of heavy-metal concentrations in the soft tissues. The aim of our present paper is to provide a review of how heavy metals are quantified in clams, mussels, and oysters. We do this by evaluating sample-preparation methods (i.e., tissue digestion / extraction and analyte preconcentration) and instrumental techniques (i.e., atomic, fluorescence and mass spectrometric methods, chromatography, neutron activation analysis and electrochemical sensors) that have been applied for this purpose to date. Application of these methods, their advantages, limitations, challenges and expected future directions are discussed.